Continuous-time filters currently constitute subject matter of high interest because of the increase of high frequency integrated systems. In order to produce an active first-order continuous-time filter two approaches are generally used: a first open loop circuit structure (shown in FIG. 1) with a transconductance amplifier A1 and a capacitor C11 in parallel with a resistance R11 and a second closed loop circuit structure (shown in FIG. 2) with an amplifier A2 and a grid formed by a resistance R22 and a capacitor C22. The first circuit structure is also called Gm-C active filter while the second circuit structure is called R-C active filter.
The first circuit structure has the advantages of high velocity and low consumption but has the problems of a limited dynamic range, low linearity and it is sensitive to the parasitic capacitances both in input and in output.
The second circuit structure has the advantages of excellent linearity and good insensitivity to the parasitic capacitances but has the disadvantage of a considerably reduced frequency response in comparison to the first circuit structure.
A second-order continuous-time filter is shown in FIG. 3. The filter has a differential structure having a differential input i+, i− and a differential output O+, O−. The filter comprises only one operational amplifier of the ideal type whose unitary-gain frequency is very high. The arrangement of the circuit elements, resistances and capacitors, is fixed so as to guarantee a very wide frequency band and precision of the response in frequency. Nevertheless the circuit structure presents the disadvantage of having high consumption of energy.
According what is needed is a method and system to over come the shortcomings and problems encountered in the prior art and to provide a continuous-time filter that has low power dissipation and good linearity